With increasing of communication traffic, 3rd Generation Partnership Project (3GPP) licensed frequency spectrums become insufficient to provide higher network capacity. In order to further improve the utilization of frequency spectrum resources, unlicensed frequency spectrum such as 2.4 GHz and 5 GHz frequency bands can already be used, in the prior art. These unlicensed frequency spectrums are currently mainly used by Wi-Fi, BLUETOOTH™, radar, medical, and other systems. In order to use the Long Term Evolution (LTE) standard on unlicensed frequency bands, 3GPP proposed a concept of LTE Assisted Access (LAA) to use unlicensed frequency spectrums with the help of LTE licensed frequency spectrums. The unlicensed frequency spectrum can have two working modes. One is the supplemental downlink (SDL), which has only downlink transmission subframes; the other is the time-division duplex (TDD) mode, and both uplink and downlink include transmitting subframes.
In addition, existing access technologies on an unlicensed frequency spectrum, such as WI-FI, are vulnerable to interference. In order to avoid interference, the Wi-Fi system is designed with many interference avoidance rules, such as carrier sense multiple access/collision detection (CSMA/CD) method. The basic principle of the CSMA/CD method is to monitor whether there are other access points (APs) or terminals on the periphery sending/receiving signaling or data before an AP of Wi-Fi or a terminal sends signaling or data. If there are other APs or terminals on the periphery which are sending/receiving signaling or data, monitoring is continued until no signaling or data is sent or received. Otherwise, if there are no other APs or terminals on the periphery that are sending/receiving signaling or data, a random number is generated as a waiting time. During the waiting time, if no signaling or data transmission is detected, the AP or the terminal may begin sending signaling or data after the waiting time is elapsed.
Good orthogonality in the LTE network ensures a low interference level, thus there is no need to consider whether there are other base stations or other users around which are transmitting data, in the uplink and downlink transmissions of the base station and the user. If the LTE is used on an unlicensed frequency band, there is no need to consider whether other devices are using the unlicensed frequency band. In such a situation, Wi-Fi device is subjected to great interference. As long as there is a service, the Wi-Fi device will transmit data. No monitoring rule exists. An idle state of the channel can be detected only after transmission of an LTE service is completed. After that, transmission can be carried out.
Therefore, when the LTE uses the unlicensed frequency band, one key point is to ensure that the LAA can coexist with the existing access technologies (such as Wi-Fi) on a fair-friendly basis. However, there is no listen before talk (LBT) mechanism to avoid collisions in the traditional LTE system. In order to better coexist with Wi-Fi, an LBT mechanism is needed for the LTE. In this way, if a channel is detected to be busy when the LTE uses the unlicensed frequency spectrum, the frequency band cannot be occupied. If the channel is detected to be idle when the LTE network uses the unlicensed frequency spectrum, the frequency band can be occupied.
However, it is found that when the unlicensed frequency spectrum is used in the TDD mode in the conventional technology, since uplink and downlink configurations of the traditional TDD are fixed, a ratio of uplink and downlink time slots is not flexible enough. When downlink data are sent, if uplink and downlink transitions occur due to fixed uplink and downlink configurations, channel resources may be snatched by a Wi-Fi device, and the downlink data transmission process may be interrupted frequently. Therefore, uplink and downlink configurations in a TDD mode in traditional technology are not flexible and the transmission efficiency is not high.